The invention concerns long half-life variants of the OB protein. In particular, the invention concerns OB protein-immunoglobulin chimeras, and compositions comprising and methods for administering them. The invention further relates to a method for treating obesity by administering a long half-life variant of the OB protein, such as, an OB protein-immunoglobulin chimera.
Obesity is the most common nutritional disorder which, according to recent epidemiologic studies, affects about one third of all Americans 20 years of age or older. Kuczmarski et al., J. Am. Med. Assoc. 272, 205-11 (1994). Obesity is responsible for a variety of serious health problems, including cardiovascular disorders, type II diabetes, insulin-resistance, hypertension, hypertriglyceridemia, dyslipoproteinemia, and some forms of cancer. Pi-Sunyer, F. X., Anns. Int. Med. 119, 655-60 (1993); Colfitz, G. A., Am. J. Clin. Nutr. 55, 503S-507S (1992). A single-gene mutation (the obesity or xe2x80x9cobxe2x80x9d mutation) has been shown to result in obesity and type II diabetes in mice. Friedman, Genomics 11, 1054-1062 (1991). Zhang et al., Nature 372, 425-431 (1994) have recently reported the cloning and sequencing of the mouse ob gene and its human homologue, and suggested that the ob gene product may function as part of a signalling pathway from adipose tissue that acts to regulate the size of the body fat depot. Parabiosis experiments performed more than 20 years ago predicted that the genetically obese mouse containing two mutant copies of the ob gene (ob/ob mouse) does not produce a satiety factor which regulates its food intake, while the diabetic (db/db) mouse produces but does not respond to a satiety factor. Coleman and Hummal, Am. J. Physiol. 217, 1298-1304 (1969); Coleman, Diabetol 9, 294-98 (1973). Recent reports by three independent research teams have demonstrated that daily injections of recombinant OB protein inhibit food intake and reduce body weight and fat in grossly obese ob/ob mice but not in db/db mice (Pelleymounter et al., Science 269, 540-43 [1995]; Halaas et al., Science 269, 543-46 [1995]; Campfield et al., Science 269, 546-49 [1995]), suggesting that the ob protein is such a satiety factor as proposed in early cross-circulation studies. The results of these first studies leave many questions unanswered, and show a number of as yet unresolved discrepancies. For example, while modest effects of daily injections of the ob protein on food intake and body weight were reported in lean mice, there was a significant reduction in body fat as assessed by carcass composition in one (Halaas et al., supra) but not in another (Pelleymounter et al., supra) of these reports, despite equivalent decreases in body weight. Furthermore, Pelleymounteobobr et al., supra observed that, for reasons unknown, ob/ob mice treated with a 0.1 mg/kg/day dose of the OB protein actually increased their body weight by 17.13%, while the weight reduction in the obese mice that received a 1 mg/kg/day dose of ob was rather moderate. The receptor or receptors of the ob protein are as of yet unidentified. While the existence of peripheral receptors cannot be ruled out at this time, the recent report that an increased expression of the ob gene in adipose tissue of mice with hypothalamic lesions does not result in a lean phenotype suggests that the OB protein does not act directly on fat cells. Maffei et al., Proc. Natl. Acad. Sci. 92, 6957-60 (1995). Researchers suggest that at least one OB receptor is localized in the brain.
The present invention is based on the observation that the OB protein is significantly more effective at reducing body weight and adipose tissue weight when delivered as a continuous subcutaneous infusion than when the same dose is delivered as a daily subcutaneous injection. The invention is further based on the unexpected finding that a chimeric protein, in which the OB polypeptide is fused to an immunoglobulin constant domain, is strikingly more potent in reducing the body weight and adipose depots than native human OB, when both proteins are administered by subcutaneous injection once a day. The latter observation is particularly surprising since the OB proteinxe2x80x94immunoglobulin chimera due to its large molecular weight, is not expected to be able to cross the blood-brain barrier, and reach the OB receptor which is believed to be located in the brain.
In one aspect, the invention concerns long half-life derivatives of OB proteins, compositions containing them, and their administration for the treatment of conditions associated with the abnormal expression or function of the OB gene, such as obesity.
In another aspect, the invention concerns chimeric polypeptides comprising an OB protein amino acid sequence capable of binding to a native OB receptor linked to an immunoglobulin sequence (briefly referred to as OB-immunoglobulin chimeras or immunoadhesins). In a specific embodiment, the chimeric polypeptides comprise a fusion of an OB amino acid sequence capable of binding a native OB receptor, to an immunoglobulin constant domain sequence. The OB portion of the chimeras of the present invention preferably has sufficient amino acid sequences from a native OB protein to retain the ability to bind to and signal through a native OB receptor. Most preferably, the OB protein retains the ability to reduce body weight when administered to obese human or non-human subjects. The OB polypeptide is preferably human, and the fusion is preferably with an immunoglobulin heavy chain constant domain sequence. In a particular embodiment, the association of two OB polypeptide-immunoglobulin heavy chain fusions (e.g., via covalent linkage by disulfide bond(s)) results in a homodimeric immunoglobulin-like structure. An immunoglobulin light chain may further be associated with one or both of the OB-immunoglobulin chimeras in the disulfide-bonded dimer to yield a homotrimeric or homotetrameric structure.
The invention further concerns nucleic acid encoding chimeric polypeptide chains of the present invention, expression vectors containing DNA encoding such molecules, transformed host cells, and methods for the production of the molecules by cultivating transformant host cells.
In another embodiment, the invention concerns a method of treating a condition associated with the abnormal expression or function of the OB gene by administering a therapeutically effective amount of a long half-life variant of an OB protein, such as an OB-immunoglobulin chimera. The invention specifically concerns a method of treating obesity.
In yet another embodiment, the invention concerns a composition for the treatment of a condition associated with the abnormal expression or function of a native OB gene, such as obesity, comprising an effective amount of a long half-life OB protein variant, such as an OB-immunoadhesin chimera.